Recovering oil by injecting hot CO2 into a reservoir containing swelling clay

Abstract

In a heavy oil reservoir containing water-sensitive clay which impedes injections of either steam or cold CO2, oil is produced by injecting CO2 vapor at more than about 130 DEG F. at a pressure below the critical pressure for the CO2 or fracturing pressure for the reservoir.

What is claimed is: 
     
       1. In a process for recovering oil by injecting fluid into an oil containing reservoir for increasing the mobility of the oil and displacing it toward a product location, where the reservoir is one in which a combination of reservoir properties inclusive of a permeability of about 50 to 150 md and swelling clay concentrations of about 25 to 35 percent interact to significantly impede injections of unheated or heated aqueous fluid or unheated CO 2 , an improvement for injecting fluid capable of providing greater rates of flow into the reservoir and greater rates of oil displacement within the reservoir comprising: injecting as said fluid a fluid consisting essentially of gaseous CO 2  at a temperature of about 130° to 160° F. which is high enough to heat the rocks near the well to an extent significantly reducing said flow impeding interaction of permeability and high swelling clay content of the rocks and thus increasing the mobility of the gaseous CO 2  within the reservoir at pressure and temperature conditions below those productive of the critical state for the injected gaseous fluid and below the fracturing pressure for the reservoir.   
     
     
       2. The process of claim 1 in which the CO 2  concentration of the injected fluid is at least about 90 percent. 
     
     
       3. The process of claim 1 in which the CO 2  is injected and fluid is produced in a cyclic process. 
     
     
       4. The process of claim 1 in which the CO 2  is injected through one well and fluid is produced from another well.